The field of the invention is systems and methods for magnetic resonance imaging (“MRI”). More particularly, the invention relates to systems and methods for using stimulated echo based mapping (STEM) imaging using magnetic resonance.
Quantitative multi-parametric MRI may enable improved diagnosis and treatment monitoring in various applications. Mapping of relaxation and diffusion parameters may enable advanced characterization of healthy and diseased tissue, with emerging clinical and research applications. Indeed, quantitative mapping of T1, T2, and apparent diffusion coefficient (ADC) has multiple previously proposed and potential applications, including in brain, cardiac, breast, and prostate imaging. Further, quantitative MRI methods may facilitate comparison of data longitudinally or between centers, as required for effective longitudinal treatment monitoring and multi-center clinical trials.
Mapping of relaxation and diffusion parameters is typically performed using multiple separate acquisitions, including one or several relaxometry pulse sequences and a separate diffusion-weighted imaging (DWI) pulse sequence. However, the need for multiple separate acquisitions using multiple pulse sequences is often not practical for clinical applications, due to long acquisition times and the challenges of obtaining co-registered parametric maps. Therefore, simultaneous mapping of relaxation (e.g., T1 and T2) and diffusion (e.g., ADC) parameters based on a single acquisition sequence is highly desirable in order to provide rapid and co-registered quantitative multi-parametric MRI.
Previous studies have explored simultaneous T1, T2 and ADC mapping with methods including diffusion-weighted Dual-Echo Steady State (DESS) and MR Fingerprinting (MRF). However, these previously-proposed techniques face substantial limitations. For the DESS method, the signal from steady-state sequence is complicated to model, especially with diffusion encoding, which may result in inaccuracy and large variance in diffusion measurements. Also, though preliminary results have shown promise for MRF with simultaneous ADC mapping, probing diffusion within the MRF framework can be challenging and may be subject to multiple confounding factors.
Stimulated-echo (STE) based simultaneous T1, T2 and ADC mapping is a promising approach to overcome the limitations of previous techniques. The STE diffusion weighted imaging (DWI) pulse sequence enables the modulation of T1, T2 and diffusion weighting by varying the mixing time (TM), echo time (TE) and b-values, respectively. As a result, by acquiring multiple (at least four) STE images with varying TM, TE, and b-values, simultaneous co-registered mapping of T1, T2 and ADC is possible. STE has been used for MR spectroscopy-based relaxometry and DWI. However, the lack of a reliable and efficient simultaneous T1, T2 and ADC mapping technique continues to be an important unmet need.
Thus, it would be desirable to have a system and method for rapid and co-registered mapping of T1, T2 and ADC that overcomes the problems facing those attempts described above.